1. Field
The present invention relates to a disc apparatus that reads data from a disk and writes data in the disk based on a command from an external device and to an advance data reading method thereof.
2. Description of the Related Art
A general disk apparatus reads data from a disk in the disk apparatus and writes data in the disk based on a command issued from an external device, such as a host computer. The disk apparatus performs a single reading or writing process per command.
The reading or writing process performed by the general disk apparatus is explained below with reference to FIGS. 10A to 10D. For example, as shown in FIG. 10A, even if a data item consists of α successive bytes on a file, the data item is divided by a maximum frame size of x bytes as long as α is larger than x (α=x+x+x+y).
As shown in FIG. 10B, upon receipt of a read command from the host computer, the disk apparatus reads the data based on Startaddress (hereinafter, “Sadd”) indicative of a start point of the frame and Endaddress (hereinafter, “Eadd”) indicative of an end point of the frame, which are included in the read command.
On the other hand, as shown in FIG. 10C, upon receipt of a write command from the host computer, the disk apparatus writes the data based on the Sadd and the Eadd, which are included in the write command.
The disk stores therein frames specified by the addresses Sadd1/Eadd1, Sadd2/Eadd2, Sadd3/Eadd3, and Sadd4/Eadd4. Even though the four frames originally formed a single data item, the disk apparatus does not always store the frames successively; the frames can be stored separately as shown in FIG. 10D. FIGS. 10A to 10D are schematic diagrams for explaining a process of reading and writing data in a disk apparatus according to a conventional technology.
A process performed by the above disk apparatus is explained below with reference to FIG. 11. Upon receipt of the read command from the host computer (see (1) in FIG. 11), the disk apparatus determines whether a requested data item is stored in a buffer (see (2) in FIG. 11).
If the requested data item is not stored in the buffer, the disk apparatus reads the requested data item in the disk and stores it in the buffer (see (3) and (4) in FIG. 11). The disk apparatus then sends the data item from the buffer to the host computer (see (5) in FIG. 11). On the other hand, if the requested data item is stored in the buffer, the disk apparatus immediately sends the data item from the buffer to the host computer. FIG. 11 is a schematic diagram for explaining a process performed by a configuration of the disk apparatus according to the conventional technology.
With the disk apparatus described above, because the disk apparatus accesses the disk after receiving the read command, it takes a certain time to read the data item. Therefore, to reduce an access time for reading the data, various technologies have been disclosed. For example, Japanese Patent Application Laid-open No. 2001-14109 discloses a disk apparatus that classifies the weight of significance of data items read from a storing medium such as a disk, and that stores the data items in a buffer in the descending order of the weight. Upon receipt of the read command from the host computer, the disk apparatus reads the requested data item from the storing medium, and sends the data item to the host computer. In other words, in the anticipation that the addresses of the requested read command are stored successively, the disk apparatus reads data and store the data in the buffer in advance, and sends the data from the buffer if the addresses are actually successive, thereby increasing throughput rate of the data reading.
However, the disk apparatus described above still requires time to access the data. Specifically, if the continuous frames of the requested data item are not stored at successive addresses, the disc apparatus needs to receive the read command from the host computer before acquiring the data item, and therefore the disk apparatus described above still takes the time to access the data.